Packaged HVAC units are known devices for heating, cooling, and ventilating spaces. Such units typically operate by drawing in air using an air mover housed within the packaged unit, cooling or heating and/or dehumidifying that air, and delivering it to the space. A packaged HVAC unit can be housed directly within the space to be conditioned, allowing for ease of installation. Such devices can be especially useful in high-occupancy spaces such as classrooms and the like. In general, but especially in these type of applications, reducing or minimizing the audible noise associated with the operation of HVAC equipment is desirable.
In some cases, a packaged HVAC unit can consist of a vertically oriented unit that is designed and constructed to occupy a majority of the floor-to-ceiling height of the space to be conditioned, thereby minimizing the wall length necessary to accommodate the unit. Such a design can advantageously direct the air flow through the HVAC unit in an overall upward direction, so that the conditioned air is directed from the top of the unit. In installations where ceiling ductwork is available to receive the flow of conditioned air and to distribute it through the space to be conditioned, such a packaged unit design can be particularly well-suited.
In addition to allowing for uniform air distribution, the additional flow length provided by ductwork is known to reduce the ambient noise associated with the HVAC unit's operation. Such a packaged HVAC unit typically includes one or more noise-producing components, such as, for example, the electric motor powered air mover. Audible noise produced by such components can be carried out of the packaged HVAC unit along with the flow of air. The pressure vibrations in the air are absorbed by the walls of the ductwork, thereby attenuating the audible noise and enabling quiet operation.
However, in many cases such ceiling ductwork is not available, and the air must be delivered directly into the conditioned space from the location of the packaged HVAC unit. In those cases, a discharge plenum is typically attached to the outlet of the packaged HVAC unit for that purpose, often filling the space between the top of the packaged unit and the ceiling. Vents provided in the discharge plenum allow for the flow of air from the packaged HVAC unit to be directed into the conditioned space. However, such a typical installation is not able to provide the noise attenuation that installed ductwork can provide. Thus, there is still room for improvement.